Having WiFi enabled shouldn't affect a sideloaded book. It could affect a downloaded kepub as the device syncs the status to the server at particular points.
So what is happening is that you are reading a book, when you finish a screen of text, you tap the screen and another screen is displayed. You keep doing this but after a few screens it returns to the first screen worth of text. And that screen is the first screen for a particular page number. Is that correct?
I can't think of a reason, just some questions:
- Can you break out of the cycle?
- Does using the navigation bar to step a screen forward help?
- What about swiping instead of tapping?
- What happens if you page backwards?
- What happens if you close and reopen the book on
- Are you using the extended driver in calibre?
- Have you checked them with epubcheck or another validater?
- What firmware version? You said you have done a factory reset, so I should be 3.0.1. Or are you using something else?
I don't know if any of that will help, but hopefully it will get us thinking.